Perhaps I'm wrong -- but somebody will have to use more than theoretical arguments to make/prove their point

And you have the perfect opportunity to do just that.
Grab a file and have at it.
You the one that insists the fit doesn't matter, not me.

BTW care to see what CZ has to say about the fit?
This is what the kadet manual has to say about fitting.

"To ensure correct functioning and high accuracy of fire, it is necessary to fit the CZ 75 KADET adapter with minimal clearances in the guide rails in the pistol on which the adapter will be used. The actual procedures are d escribed below."
Page 24 of the manual.